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  • Another Lesson

    I lost the chuck mount I've making over those infernal 2.25x8tpi threads. Being a natural born chicken I was running them at 60 rpm, as low as I can go, just because I wanted to keep things slow. I shoulda realized when I had to hold the cross up against the threadstop and the turret just about danced off the end of the bed that we had a little too much vibration goin' on ....

    Imagine my surprise when I shut it down for a look. Well I never cut a full 8 tpi before and who knew a chattered up thread could have such a pretty jeweled look to it anyway? LOL! Then I tried to clean it up which turned out to be the 1st step down the slippery slope to disaster.

    I eventually upped the speed to 100 rpm and found it cut fine there. I'll know what to do next time.

    So who sells cast semi-finished backplates?

    SP

  • #2
    MSC industrial supply. Is one Travers Tool , and just about any supplier.
    Every Mans Work Is A Portrait of Him Self
    http://sites.google.com/site/machinistsite/TWO-BUDDIES
    http://s178.photobucket.com/user/lan...?sort=3&page=1

    Comment


    • #3
      threading

      Don't feel too bad. Last night I spent half the night making a nut I have mede 100 times before. 2" 8tpi inside threads. Bar was rubbing about 5 inches in so I tried to adjust it and ended up throwing away half a days work.
      Some times it happens.

      mark61

      Comment


      • #4
        http://www.cdcotools.com/

        CDCO Machinery Corp
        1129 Tower Rd.
        Schaumburg, IL 60173 Tel: (800) 417-2305 (847) 592-6130
        Fax: (888) 731-8949 (847)592-6131




        Chuck Dia Back Plate Thread Item No. Price
        4" 1x10 25450 $29.00
        4" 1-1/2x8 25451 $29.00
        5" 1x10 25452 $32.00
        5" 1-1/2x8 25453 $32.00
        6" 1-1/2x8 25454 $38.00
        6" 2-1/4x8 25455 $38.00
        8" 1-1/2x8 25456 $49.00
        8" 2-1/4x8 25457 $49.00
        "The men the American people admire most extravagantly are the greatest liars; the men they detest most violently are those who try to tell them the truth." H. L. Mencken

        "All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."

        "When fear rules, reason and logic are ruled out."

        Comment


        • #5
          Internal boring and threading

          Originally posted by mark61
          Don't feel too bad. Last night I spent half the night making a nut I have mede 100 times before. 2" 8tpi inside threads. Bar was rubbing about 5 inches in so I tried to adjust it and ended up throwing away half a days work.
          Some times it happens.

          mark61
          What ever you do - don't give up.

          We've all had a thing we've done "lots of times" go wrong.

          I think the 60 RPM mentioned previously was about right. I'd have tried a "test-piece" to refine my processes before I got into the "finished" article.

          This post should really get the purists and "traditionalists" going - so here goes.

          It might come as a surprise but when you "know" your machine you can tell a lot about how it is going just by "feel" - just resting the fingers or palm of your hand on the tool-post or head-stock. If you can do it with your truck or bike - why not with your lathe, mill, drill etc?

          Using a lot of the correct cutting fluid solves or prevents a lot of problems as well - as do "honed" tools.

          "Yeah but that oldtiffie is "different"" I hear some say - well for what its worth, that's a "given".

          There has been a lot of comment about getting lathe tools on correct centre height. Fine (not always - see later) for external work but not necessarily for internal work.

          "Cr*p", "why" et al ......................... I hear.

          If you think about it, if the "outside" tool at centre height "dips" under load (which it will) it will tend to move away from the work and so minimise load and damage. With internal work (boring, threading etc.) the tool should be set a little above centre so that when it "dips" under load (which is does and will) it moves away from the job and tends to reduce the load and "digging-in". On or under centre and it "digs in".

          Wrong? Perhaps - but draw it up on your CAD program.

          And having the tool a little above (or in the case of external work - below) centre will not make much or any perceived difference at all to the shape of the thread.

          No? Well try that on the CAD program as well.

          Finished? Not quite.

          A lot of us will use the "turn the compound rest and top slide half the angle of the thread and feed in with the top slide" method for external threads but not for internal. Why not? Just "boring it in" and using a longer cutting edge is asking for the same problems as occur with "plunging in" with form-turning and "parting off".

          "Any bl**dy more?" Yep.

          First of all check the gibs and tool post etc. and tighten where necessary.

          Too many put a "flat" on the top of the tool with little or no side rake - and if there is side rake it is meant only for one (usually the leading) flank of the thread. Usually you can "get away" with it on the leading flank but in both cases the tool has varying degrees of negative rake on the "trailing" flank.

          So - what to do?

          1.
          Use a "plunge" cutter such as a "parting tool" or grooving tool with side rake equal to the thread helix angle to take out the bulk of material with least cutting face width and then clean it out.

          2.
          put a side rake equal to the helix angle of the thread on the screwing tool and just cut one flank at a time.

          Now "where did he get all that from" you may well ask.

          Well I live in a bat cave "down here" suspended in the dark from the ceiling with my head immersed in the "stuff" on the cave floor (as you can imagine) and the methods I got were in the "stuff on the floor" (what else?). Stuff that grows in it ain't all that bad either.

          Comment


          • #6
            I took a look at CDCO and Travers, thanx for the links, but being a glutton for punishment and a stubborn SOB to boot, I opted for a piece of ductile iron for the next go round. Brother's discount at McMaster gets me a 6"x2" for less than $20. No shipping.

            It's all about learning and this 2.25x8 has reached the personal vendetta stage.

            SP

            Comment


            • #7
              Keep it up

              Originally posted by pntrbl
              I took a look at CDCO and Travers, thanx for the links, but being a glutton for punishment and a stubborn SOB to boot, I opted for a piece of ductile iron for the next go round. Brother's discount at McMaster gets me a 6"x2" for less than $20. No shipping.

              It's all about learning and this 2.25x8 has reached the personal vendetta stage.

              SP
              I'd have said "challenge" as "vendetta" brings to mind large swarthy blokes carrying violin cases with violins in them - not (like Al Capone's "friends").

              I've had to pick myself up and dust myself off all too often and "get back into it" as you have done.

              If you think you were proud of the first effort (as you were entitled to be) it's nothing compared to the satisfaction you'll get out of getting this "right".

              There's some truth in the old maxim:
              The bloke who never made a mistake never made anything.

              Comment


              • #8
                That's me, sometimes a project just becomes a personal challenge, may not actually need the product anymore, but it gave me enough grief that I just HAVE to finish it.

                Ken

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